Grinding machines

ABSTRACT

A GRINDING MACHINE COMPRISES A GRINDING A WHEEL FOR GRINDING A CIRCUMFERENTIAL SURFACE OF A WORKPIECE OF CIRCULAR CROSS-SECTION SUCH AS A STEEL ROLL, TRAVERSING MEANS ADAPTED TO EFFECT RELATIVE LONGITUDINAL TRAVERSING MOVEMENT IN THE DIRECTION OF THE AXIS OF THE WORKPIECE, BETWEEN THE GRINDING WHEEL AND THE WORKPIECE, ROTARY MEANS FOR ROTATING THE WORKPIECE WHILE IT IS BEING GROUND, GAUGING MEANS FOR DETERMINING, WHILE THE GRINDING WHEEL IS GRINDING THE WORKPIECE, ANY DIFFERENCE BETWEEN A DATUM VALUE AND THE DIAMETER OF THE PARTICULAR CIRCUMFERENCE OF THE WORKPIECE ON WHICH THE GRINDING WHEEL IS ACTING MEANS, CONTROLLED BY THE GAUGING MEANS, FOR ADJUSTING THE POSITION OF THE GRINDING WHEEL IN A SENSE TO BRING SAID DIFFERENCE TO A PREDETERMINED VALUE, A MOVABLE DATUM MEMBER PROVIDING SAID DATUM VALUE, A CAM ROTATION OF WHICH IS ADAPTED TO EFFECT ADJUSTMENT OF THE POSITION OF SAID DATUM MEMBER, THEREBY ADJUSTING THE DATUM VALUE, CONTROL MEANS, ACTUATED BY THE TRAVERSING MEANS, AND   CONTROLLING THE CAM DRIVING MEANS IN A MANNER TO RELATE THE ROTATIONAL POSITION OF THE CAM TO THE POSITION OF THE TRAVERSING MEANS, THE CONTROL MEANS BEING ADJUSTABLE IN A MANNER TO VARY THE RELATION BETWEEN THE ROTATIONAL POSITION OF THE CAM AND THE POSITION OF THE TRAVERSING MEANS.

R. AGLADSTONE GRINDING MACHINES klan. f5, 1'971 9 Sheets-Sheet l FiledFeb. 5, 1969 Inventor Robert Gladstone rey? o Jan. 5, 1971 Filed Feb. 5,1969 R. GLADsToNE 3552,06

GRINDING MACHINES 9 sheets-sheet 2 o5 Inventor Robert Gladstone s T C mA m Lm I R Jan. 5, 1971 9 Sheets-Sheet 5 Filed Feb. 5 1969 Jan. 5, 1971l GLAbsTQNE GRINDING MACHINES 9 Sheets-Sheet A Filed Feb. 5 1969Inventor Robert Gladstone j; I My g/Q45@ Jan. 5, 1971 R. GLADsToNEGRINDING MACHINES 9 Sheets-Sheet 5 Filed Feb. 5 1969 Inventor RobertGludsone Z/fA 1&11'151971 'l R. GLADsToNE 3552,96

GRINDING MACHINES Filed Feb. 5, 1969 9 Sheets-Sheet 6 Inventor RobertGladstone Jan. 5, 1971 R. GLADsToNE 3,552,065

GRINDING MACHINES Filed Feb. s, 1969 9 sheets-sheet 7 I 75 DDD "Wlnvenior D00 O q Robert Gludsone /f/Q; @Wwf/yf' 'j "Tilt 1971 l R.GLADSTON 3,552,066

GRINDNG MACHINES Filed-Feb. 5; 1969 y 9 Sheena-shew, a

A 2 a 4 s s 7 e s :au f2 2 *X*- OOOO OOO "Y- OOOOO "z- OOOOO X OOOOO 4075PM/(5P o o o o o o o o o o o o o Z- OO O OOO() v2/rr- O C) C) O O O Geax/2l l 1 2 2 2 2 3 a a a 4 4 00000 OO-OOO OOOOOOOOOO OOOOOOOO OOOOOOOO ln for Robert odsone Jan. 5, 1971 R.G1 ADsToNE 3,552,065

GRINDING lvLAcnLIINEs` Filed Feb. 1969 9 sheets-sheet 9 Inventor RobertGladstone Und States Patent 3,552,066 GRINDING MACHINES RobertGladstone, Weybridge, Surrey, England, asslgnor to Wiggins TeapeResearch & Development Limited, London, England, a British company FiledFeb. 5, 1969, Ser. No. 796,705

Int. Cl. B24b 5/04 U.S. Cl. 51-49 6 Claims ABSTRACT F THE DISCLOSURE Agrinding machine comprises a grinding wheel for grinding acircumferential surface of a workpiece of circular cross-section such asa steel roll; traversing means adapted to effect relative longitudinaltraversing movement in the direction of the axis of the workpiece,between the grinding wheel and the workpiece; rotary means for rotatingthe workpiece while it is being ground; gauging means for determining,while the grinding wheel is grinding the workpiece, any differencebetween a datum value and the diameter of the particular circumferenceof the workpiece on which the grinding wheel is acting; means,controlled by the gauging means, for adjusting the position of thegrinding wheel in a sense to bring said difference to a predeterminedvalue; a movable datum member providing said datum value; a cam rotationof which is adapted to effect adjustment of the position of said datummember, thereby adjusting the datum value; control means, actuated bythe traversing means, and controlling the cam driving means in a mannerto relate the rotational position of the cam to the position of thetraversing means, the control means being adjustable in a manner to varythe relation between the rotational position of the cam and the positionof the traversing means.

The invention relates to grinding machines, and is more particularly,but not exclusively, concerned with grinding machines for grindingaccurately to shape and size steel rolls for use, for example, inpaper-making processes.

The invention is an improvement on known apparatus for grinding parallelor cambered rolls to a relatively high degree of accuracy. The knownapparatus derives the ultimate camber form of a roll from a cam whoseprofile is cut on a large scale according to the desired law.

In the known apparatus, the cam is rotated by an electrical step by stepmotion generated by the traverse mechanism of a grinding machine, sothat when grinding a roll of the greatest length for which the machinecaters, the cam is rotated through its complete working track as thegrinding head makes a complete half traverse from the centre to eitherend of the roll. lf for some reason a roll of greater length were to beground, a complete half traverse would result in the cam being rotatedbeyond the end of its working track, with unpredictable results on thecamber produced at the extreme ends of the over-length roll.` Where aroll shorter than the maximum is to be ground, there is no alternativebut to camber it according to the cam law as generated over a part onlyof the working track proportional to the length of roll. This workingtrack may for example generate a sine function between limits of 0 andsome preferred value Y (usually in the region of 70), and this preferredvalue is reached at either end of a roll of the designed maximum length.If X/ Y represent the length ratio of any shorter roll compared with themaximum, then if such shorter roll is ground with camber, at either endof the camber form will reach the value given by Xa instead of thepreferred value Y".

Ece

There is accordingly in the first place a requirement for a means ofensuring the complete rotation of the camber generating cam during ahalf traverse of rolls of any length that may have to be ground.

In the second place there is also a requirement to produce at willcamber forms (e.g. parabola, ellipse, etc.) according to laws other thanthat according to which the cam has been cut.

The present invention provides means which may be arranged to meet boththese requirements.

According to the invention there is provided a grinding machinecomprising: a grinding wheel for grinding a circumferential surface of aworkpiece of circular crosssection; traversing means adapted to effectrelative longitudinal traversing movement, in the direction of the axisof the workpiece, between the grinding wheel and the workpiece; rotarymeans for rotating the workpiece while it is being ground; gauging meansfor determining, while the grinding wheel is grinding the workpiece, anydifference between a datum value and the diameter of the particularcircumference of the workpiece on which the grinding wheel is acting;means, controlled by the gauging means, for adjusting the position ofthe grinding wheel in a sense to bring said difference to apredetermined value; a movable datum member providing said datum value;a cam rotation of which is adapted to effect adjustment of the positionof said datum member, thereby adjusting the datum value; and controlmeans, actuated by the traversing means, and controlling the cam-drivingmeans in a manner to relate the rotational position of the cam to theposition of the traversing means; the control means being adjustable ina manner to vary the relation between the rotational position of the camand the position of the traversing means.

The control means may comprise: an information carrier; reading meanspast which the information carrier is moved; and drive means for movingthe information carrier past the reading means; the drive means beingcontrolled by said traversing means so as to move in synchronismtherewith; and the reading means controlling the cam-driving means inaccordance with a predetermined programme carried by the informationcarrier.

The drive means for the information carrier may comprise a synchroreceiver motor driven by a synchrotransmitter which is driven in turn bythe traversing means.

The traversing means, synchro transmitter, synchro receiver motor, andinformation carrier are preferably all driven with a step-by-stepmotion. For example, the cam-driving means may comprise an electricmotor driven with a ste-y-by-step motion by signals imparted to thereading means by the information carrier.

The information carrier may comprise punched tape.

A preferred embodiment of the invention will now be described by way ofexample and with reference to the accompanying drawings of which:

FIG. 1 is a schematic drawing of the elements of a grinding machine anda control system therefor;

FIG. 2 is an elevation, sectioned in part, of the measuring andreference heads of FIG. l;

FIG. 3 is a circuit diagram of the comparator circuit used with theapparatus of FIG. 1;

FIG. 4 is a circuit diagram of the second and third amplifiers of FIG.l; and

FIG. 5 is a circuit diagram of the first amplifier of FIG. 1.

Also, a further embodiment of the invention will be described withreference to FIGS. 6 to l5 of the accompanying drawings of which:

FIG. `6 shows diagrammatically the elements of a grinding machine and acontrol system therefor;

FIG. 7 shows somewhat diagrammatically the arrangement of some of theelements shown in FIG. 6, but in greater detail, in a control panel forthe system;

FIG. y8 is a theoretical circuit diagram of one of two similaramplifiers in the control system;

FIG. 9 is a theoretical circuit diagram of the input arrangements to oneof these amplifiers;

FIG. 10 is a theoretical circuit diagram of the input arrangements tothe other amplifier;

FIGS. 11 and 12. show portions of punched paper tape suitable for use asinformation carriers in the cam control apparatus;

FI'G. 13 is a front view of a tape reader suitable for use in either ofthe described arrangements;

FfI-G. 14 is a side view of the reader of FIG. 13; and

FIG. 15 is a rear View of the tape reader.

FIG. 1 shows a grinding machine 211 which acts on a workpiece 212 whichis rotated about a horizontal axis (by means not shown). The grindingmachine comprises a grinding Wheel 213 driven by a direct currentelectric motor 214 to rotate about an axis parallel to the workpieceaxis. The wheel 213 and motor 214 are mounted on a table 215 which ispivotally mounted on a saddle 216. Saddle 216 is continuously traversedalong a slide 217 on the frame of the machine by means not shown so thatin a normal traverse the saddle will move continuously from one end ofthe workpiece to the other. A position transmitter 218 carried by thesaddle 216 is driven by a pinion 219 which engages with a rack 221mounted parallel with the slide 217.

Table 215 is pivotally mounted relative to saddle 216i about an axis222, and the grinding wheel 213 is fed towards and backed away from theworkpiece 212 (in a direction perpendicular to the workpiece axis) bypivoting the table 215 about the axis 222. Such pivoting is effected bya wheel feed motor 223 which drives a cam 22.4. Cam 224 bears againstone end of a lever 225 which is pivoted on a bracket 226 of the saddle216, and the other end of which bears against a stop 227 on the table215. lRotation of cam 224 therefore raises or lowers the side of thetable 215 remote from the axis 222 and thereby feeds the grinding wheel213 towards or backs it away from the workpiece 212.

The diameter of the workpiece 212 is measured on the circumference onwhich the grinding wheel 2.13 acts, by a gauge comprising anelectrically operated measuring head 228, which is carried on a rigidframe (not shown) attached to saddle 216. This rigid frame carries alsoa micrometer adjustment screw 229l which carries a hardened anvil 231and which is adjusted in use so that the anvil 231 bears against thelower extremity of the diameter of the workpiece 212 which is measured.A similar anvil 232 bears against the upper extremity of the diameterwhich is measured, this anvil 232 forming part of the measuring head 228and being mounted on a shaft 233 to -be capable of radial movementrelative to the workpiece.

In a manner to be described with reference to FIG. 2, the measuring head22.8 gives an output signal at mains frequency, the amplitude of whichsignal is dependent upon the difference between the position of theanvil 232 and a datum position set by datum set motor 234. The datum isset in accordance with the required diameter of the workpiece, so thatthe output signal from the measuring head 228 represents the deviationof the actual diameter of the workpiece from the required diameter.

The output from the measuring head 228 is fed over line 235 to a firstamplifier 236 where it is amplified to provide an instantaneousindication of the diameter deviation on meter 237 and a permanent recordon recorder 238, where an automatic plot of diameter deviation againstamount of traverse of the grinding wheel 213 along the workpiece 212 ismade. The information regarding the amount of traverse at any moment isfed from the position transmitter 218 to a punched tape 4 digitalcontrol apparatus 389 which, in a manner to be described, transmitssignals over a line 239 to the drive motor of an apparatus 276 to bedescribed in detail later. Information regarding the amount of traverseis also fed, along the line 239, to a recorder 238.

From the first amplifier 236 the measuring head output signal is takenover line 241 to an input of a second amplifier 242, In this amplifier242 the diameter deviation is compared with the rate of grinding of the-workpiece 212 by the grinding wheel 213 and the relation between themused to derive an output which controls the speed and direction of thegrinding wheel feed motor 223. In this way the rate of grinding is madeto vary in accordance with the diameter deviation of the workpiece; alarge diameter deviation requiring a high grinding rate and consequentlya high grinding wheel feed in and a small diameter deviation meaningthat the diameter of the 4workpiece is nearly correct and a low grindingwheel feed in is required to achieve a high accuracy finish.

The rate of grinding of the workpiece 212 by the grinding wheel 213 ismeasured by measuring the load on the wheel motor 214. This is done bymeasuring the current taken by the motor 214, part of the drivingcurrent being arranged to pass through a shunt resistor (not shown) togive a direct potential signal on line 243 proportional in magnitude tothe wheel motor current. This signal is applied to an input of thesecond amplified 242, and also over line 244 to a wheel load meter 245which gives an indication of the instantaneous grinding rate.

The output of the second amplifier 242 is applied over line 246 to theinput of a motor 247, the speed and direction of which is governed bythe amplitude and phase of its input. Motor 247 is mechanically linkedto a generator 248, the output of which is applied as negative feedbackto an input 249 of the amplifier 242. This negative feed-back ensuresthe stability of the system and prevents hunting. Motor 247 is alsomechanically linked to wheel feed transmitter 251, which generatessignals that are transmitted over line 252 to wheel feed motor 223 todrive the motor 223 in a direction determined by and at a speedproportional to, the direction and speed respectively of motor 247, andthereby increase or reduce the grinding rate as necessary. An indicationof the instantaneous wheel feed position is given on wheel feed meter253, a signal for which is derived from a wheel feed position indicator254 mounted in the drive mechanism for cam 224, the signal being passedover line 255 and amplified in the first amplifier 236.

The apparatus thus far described is arranged to operate the grindingwheel 213 so as to reduce the deviation of the workpiece diameter from adatum set in the measuring head 228. When this deviation is zero nofurther feedin is applied to the grinding wheel 213 and grinding ceases.The diameter of the workpiece 212 is thus reduced to that correspondingto the datum set inthe measuring head 228. In a manner to be describedthe datum is set by the datum-set synchro receiver motor 234 which isdriven by signals sent over line 256 from a datum transmitter 257.Connected in parallel with the motor 234 is a similar datum-set motor258 of a reference head 259 which is identical to measuring head 228.This arrangement ensures that the datum value of the reference head 259changes identically and simultaneously with the datum value of themeasuring head 228 in response to signals from transmitter 257. Thedatum values of the heads 228 and 259 are set to the required value bymechanically setting the position of the feeler 261 of the referencehead 259 to correspond to the desired datum diameter of the workpiece.The output from reference head 259, which is an error signalrepresenting the deviation of the position of feeler 261 from the datumposition of datum-set motor 258, is applied over line 260 to a thirdamplifier 262. The output of amplifier 262 is applied over lines 263a todrive, through motor 263, the datum transmitter 257 and thus the datumset motor 258 (and also motor 234) in such a sense as to cancel theerror signal from reference head 259. Therefore the datum value inmotors 258 and 234 are set in accordance with the position of thereference head feeler 261, and will follow any deviations thereof.

In order to grind a workpiece to a cylindrical shape the position of thereference head feeler 261 remains constant at the required valuethroughout grinding. However, in order to grind a workpiece to a taperedor cambered profile means are provided for varying the desired datumdiameter of the workpiece as the grinding wheel traverses the workpiece,by varying the position of the feeler 261 of the reference head 259 in apredetermined manner as the saddle 216 moves along the slide 217. Thisapparatus is represented at 276 in FIG. 1 and its operation will be morefully described with reference to FIG. 7 showing the alternativearrangement. A set-up meter 299 is connected to the first amplifier 236to facilitate set-up of the apparatus.

Referring now to FIG. 2, there is shown an elevation, sectioned to theright of line AA, of the measuring head 228 and datum set motor 234. Thereference head 259 and its associated motor 258 are identical inconstruction to head 228 and motor 234 respectively except as describedbelow in respect of parts 339, 341 and 342. Housing 305 is rigidlymounted at the upper end of a rigid caliper frame (not shown) attachedto saddle 216. The caliper frame is adjustable to accommodate variousrigid workpieces, but is clamped during a grinding operation. Anvil 232bears at its lower end on the workpiece at the upper extremity of thediameter which is measured and at its upper end is secured on the end306 of shaft 233. Shaft 233 is formed integrally with armature 307 of adifferential transformer 308. The armature 307 bears a salientl pole 309which is positioned between two poles 311, 312 salient upon the stator313 of the transformer 308. The stator 313 carries two windings 314, 315and the armature 307 a single Winding 316. The armature 307 and shaft233 are suspended from housing 305 by parallel spring strips 233:1 atthe ends thereof to permit vertical movement relative to the housing 305and to the stator 313. A set-up meter 299 is connected to a receivingamplifier 236 to facilitate set-up of the apparatus.

In operation, the two stator windings 314, 315, which are composed ofequal numbers of turns are connected in series opposition and armaturewinding 316 is energised at mains supply frequency (usually 50 c.p.s.).When the the stator poles 311, 312, are symmetrically disposed about thearmature pole 309 the voltages induced in the stator windings 314, 315are exactly balanced and the resultant in the output, which is takenfrom the series combination of stator windings, is zero. Should thearmature 307 then be moved upwards by virtue of the anvil 232 movingupwardly in response to an increase in workpiece diameter, there will bemore flux linkage between the armature pole 309 and stator pole 311 thanbetween the armature pole 309 and stator pole 312, the air-gaps 317,318, between the poles having been reduced and increased respectively. Aresultant voltage will therefore be induced in the output circuit andthe sense of the windings is arranged so that this resultant voltage isin phase with the mains supply to the armature winding 316. On the otherhand, should the diameter of the workpiece decrease, the anvil 232 willdrop and allow armature 307 to drop, the armature 307 being urgeddownwardly by its weight and by the action of two springs one of whichis shown at 319 attached to one end to a pin 321 on the armature and atthe other end to a pin 322 on the housing 305.

The output of the differential transformer 308 then gives a resultantvoltage in phase or antiphase to the mains supply voltage. In each casethe amplitude of the output from the differential transformer 308 Variesin accordance with the degree of deviation of the armature 307, and thusthe anvil 232 from the balance condition.

Since the anvil 232 is held in contact with the surface of theworkpiece, the armature 307 is effectively fixed in relation to the axisof the workpiece. The output of the differential transformer 308 maytherefore be balanced to zero for any workpiece diameter within therange of the stator frame by moving the stator 313 relative to theworkpiece 2.12. `In order to alter the datum diameter at which zerooutput is obtained, provision is made to move the stator 313 relative tothe housing 305, which is fixed relative to the workpiece 212. Stator313 is suspended from housing 305 by further parallel spring strips andis biased downwardly by its Weight in conjunction with the action of twosprings, one of which is shown at 323 attached at one end to a pin 324on the stator and at the other end to a pin 325 on the housing. Thestator 3.13 is supported against this bias by a ball 326 on a lever 327.Ball 326 bears against a hardened steel anvil portion 328 of a cross-bar329 constituting part of the stator structure.

Vertical movement is applied to ball 326 and thence to stator 313 byrotation of the lever 327, which is pivotally mounted in the housing 305by a pivot pin 331. Rotation of the lever y32'7 is achieved by ahorizontal movement Vapplied at the end '332 of the lever 327 fby amicrometer screw 333. Screw 333 is threaded into the housing 305 at 334and moves horizontally as a result of rotational movement applied to itby a rigidly attached toothed gear wheel 35 which meshes with a lfurthergear wheel 3361. Gear Wheel 336 is driven by Worm gearing in gear-box337 from the output shaft 338 the datum set motor or receiver 234 (seealso FIG. 1), which comprises a stepby-step motor having a three phasefield winding connected in delta, with a salient pole rotor. Transmitter2157 is arranged to commutate a 24 volt alternating supply to any one orany pair of the three field windings of motor 234, in one of twoalternative phases, thus giving twelve alternative signals to each oneof which corresponds an unambiguous position of the rotor of the motor234. The twelve rotor positions are arranged to be spaced 30 apart andthe transmitter 257 is arranged to give two sets of successive signalscorresponding to the twelve positions in each revolution of the input tothe transmitter 257. Consequently during one half revolution of theinput to the transmitter 257, the receiver receives twelve steps.Rotation of the transmitter 257 input therefore gives a correspondingrotation of the receiver output, but at twice the speed. KIn this waythe receiver 234 follows the rotation in one direction or the other ofthe input drive shaft to transmitter 257. Receiver 258 of the referencehead 259 is similarly arranged, and once they have been set to start atzero with the transmitter 257, the two receivers 234 and 258 remainsynchronised with the transmitter and thus with each other.

Activation of the receiver motor 234 rotates the output shaft 338 toraise or allow to drop the stator 313 of the differential transformer308 and thus change the datum workpiece diameter in the mannerdescribed. In the reference head only, there is provided an output fromgear-box 337 which drives a Worm 339 which drives a worm-wheel 341. Thisworm-Wheel 341 has a pointer (not shown) mounted on its shaft 342 tomove over a fixed scale (not shown) to give an indication of theinstantaneous value of the datum diameter. A disc 343 is mounted on therotor shaft 33S of the motor 234 of the measuring head only. This disc343 may Ebe used in conjunction with the datum indicator on thereference head to re-synchronise the positions of the two heads whennecessary.

The output signal from measuring head 22'8 is passed through two cathodefollower stages of the first amplifier 2.36, it then being applied overline 241 to the input of amplifier 242. The wheel load signal is adirect current slgnal derived `from a shunt resistor in the powercircuit (indicated diagrammatically at 214e) to motor 214. The magnitudeof the wheel load signal is proportional to the grinding rate and it isapplied through line 243 to amplifier 242 to control the magnitude of asignal at mains frequency which opposes the deviation signal from themeasuring head 2'28.

FIG. 3 shows the comparator input circuit to amplifier 242. The directcurrent wheel load signal is passed via line 243 through a saturatingwinding 351 of a saturable reactor 352. Energising windings 353, 354 ofthe reactor are energised from a 24 volt A.C. supply S-S at mainsfrequency, the energising current passing through diodes 355, 356 topotentiometer 357 and thence to earth. A biasing flux is applied to thereactor 352' by passing current from a stabilized supply 358 through abiasing winding 359. The voltage from the tap of potentiometer 357 isapplied, through a wave shaping circuit 361 to the primary winding 362of a transformer 363. The other end of winding 362 is connected to thetap of a potentiometer 464, across which is applied over line 249 avelocity feed-back voltage `from generator 2418 (FIG. 1). This feed-backis negative and ensures stability of the system. The secondary 364 oftransformer 363 is connected in series in the input line 2'41 for theamplified deviation signal from the measuring head 228. Alternativemethods to that described above for deriving an A.\C. signal inproportion to the D.C. grinding wheel load signal may be employed. Forexample, a system comprising a D.C. galvanometer having a movement whichalters the setting of a differential transformer is envisaged.

The relative sense of the windings 362 and 364 is arranged so thatsignals from reactor 352 induce in Winding 364 signals which oppose thedeviation signals. The extent of the opposition thus provided isdetermined by the magnitude of the wheel load signal, since the moresaturating current there is in winding 351, the more potential isdeveloped across potentiometer 357 and the greater is the magnitude ofthe opposition signal induced in winding 364.

The error signal 4which is carried by li-ne 365 thus represents thedifference between the workpiece diameter deviation and the grindingwheel load. This error signal is applied to an amplifier which controlsthe wheel feed motor 223, the wheel being fed into the workpiece at arate dependent upon the amplitude of the error signal. However, feedingin the grinding wheel both increases the load and reduces the diameterof the workpiece. Both these factors tend to reduce the error signal, sothat the control system is stable and the grinding wheel eventuallyassumes a -no-load brushing -position at the datum diameter. A largediameter deviation requires a large grinding wheel load to balance itand reduce the error signal to zero, so that a characteristic of thesystem is that the rate of grinding automatically Varies in proportionto the deviation of the workpiece diameter from the desired datum.

In addition to the circuit described with reference to FIG. 3 the secondamplifier 242 comprises an `amplifier circuit shown in FIG. 4. The errorsignal from the line 365 is amplified in cascaded triodes 366, 367, andfinally in a push-pull output stage 369. The output from the amplifieris taken from transformer 371 and applied to the control winding ofmotor 247 (FIG. 1). Motor 247 has a reference Iwinding which is suppliedat mains frequency and phase. To obtain maximum power the lcontrolwinding must be supplied by a voltage 90 ont of phase with that acrossthe reference winding. The error signal applied to the amplifier inputis in phase or antiphase ywith the diameter deviation signal which, asdescribed, is in phase or antiphase with the mains supply. One stage ofthe required 90 lag is obtained by virtue of capacitor 372 which isconnected across `the output of triode 366 to give approximately 30 lag.This lag, together with the inherent lag of the transformer I371 and theremaining amplification stages is adjusted to 90 by a padding capacitor373 at the input of the amplifier.

Should the input signal to the amplifier be in antiphase to the mainssupply, the amplifier output would lead the reference voltage by 90 andthe motor 247 would be driven in the reverse direction to back off thegrinding wheel from workpiece. This condition would apply if for somereason the measuring head were to register a diameter less than thedatum or if the wheel load signal in winding 364 (FIG. 3) were to exceedin magnitude the diameter deviation signal. The back-off condition alsoapplies when relay RL1 is de-energised by a manually'operated off buttonat the end of a normal traverse or at the end of a partial traverse toremove a large high spot, with the contacts in the positions shown. Thismakes contact between poi-nts 2 and 3 and applies a dummy backing offsignal from line 374 to the input of the amplifier. Energisation ofrelay RL1, which is accomplished by operation of a start button on thecontroller, makes contact between points 1 and 2 and applies the errorsignal to the amplifier. Contact is made also between points 4 and 5,thereby holding relay RL1 on. Contact is broken between points 6 and 7,and this prevents a second relay RL2 from operating when relay RL1 isenergised. Relay RL2 is energised by a microswitch 250 (see FIG. 1)which closes when the grinding wheel is in its fully withdrawn position.On operation, relay RL2, which is a shut-down relay, changes over fromthe position shown and prevents any operating signal reaching the outputof the amplifier and thus the wheel feed motor 223.

The wheel feed motor 223 is a step-by-step servo receiver driven by thecommutating transmitter 251 in a manner similar to that described withreference to the servo system comprising transmitter 257 and receivers234 and 258 of FIG. 1.

'Ihe remainder of FIG. 4 shows the circuit diagram of the third, datumamplifier 262 (FIG. l). Except that no relays are provided, thisamplifier is in every respect the same as the amplifier described above.The input signal is applied over line 260 from reference head 259 :andthe output is applied to the control winding of motor 263 to rotate itsoutput shaft in one direction or the other depending upon the phase ofthe input and at a speed depending upon the magnitude of the input, asis the case with motor 247.

FIG. 5 shows the circuit diagram of the first amplifier 236 of FIG. 1.The output from the stator windings 314, 315, of the measuring headdifferential transformer 308 is applied through transformer 375 andcathode follower circuit 376 to the input of a gate 377. Gate 377 is adiode bridge connected as shown with point 378 at a reference voltage.The gate limits the range of the input to cathode follower 379 tobetween two reference values. In operation the potentiometer 381 isadjusted so that a signal equivalent to a diameter deviation of .001inch above the datum just fills the gate 377.

The output from cathode follower 379 varies in accordance with theoutput from differential transformer 308 between zero and a maximumvalue governed by gate 377, and appears across a potentiometer 382, thetap of which is connected through a primary winding 383 of a transformer384 to a tap of a potentiometer 385. The output of the circuit is takenfrom the secondary winding 386 of transformer 384 and constitutes thediameter deviation signal which is applied to the comparator circuit ofF IG. 3.

Potentiometer 382 provides that the diameter deviation signal does notexceed a predetermined maximum value which is a predetermined proportionof the maximum output from cathode follower 379. This maximum rvaluecorresponds to a maximum permissible grinding wheel motor load current.Thus the arrangement is such that the control system cannot, howeverlarge the out of balance signal from the measuring head, cause anincrease of the grinding wheel motor load current to beyond thepermissible maximum. The maximum wheel load potentiometer 382 is setempirically.

An alternating reference voltage is applied across potentiometer 385 inantiphase with the voltage across potentiometer 382. This ensures thatwhen the diameter deviation signal from the measuring head is zero,indicating that the desired datum diameter has bee-n reached, a smallapparent diameter deviation signal will still be applied to thecomparator circuit. This small signal is arranged, by empiricaladjustment of the minimum wheel load potentiometer 385, to be ofamplitude just sufiicient to balance the no-load current taken by thegrinding wheel motor when the grinding Wheel is merely brushing, but notgrinding, the work-piece. In this way a balance is obtained at the datumdiameter with the grinding wheel brushing the workpiece, no error signalbeing given by the comparator circuit of FIG. 3-

A further embodiment of the invention, differing principally from thatdescribed above in the type of measuring and reference heads employedwill now be described with reference to FIGS. 6 to 10.

In this embodiment, a grinding machine 11 acts on a workpiece 12 whichis rotated about a horizontal axis (by means not shown). The grindingmachine comprises a grinding wheel 13 driven by an electric motor 14 torotate about an axis parallel to the workpiece axis. The wheel 13 andmotor 14 are mounted on a cross-slide 15 which is fed towards and backedaway from the workpiece 12 (in a direction perpendicular to theworkpiece axis) by feed-mechanism 16 which includes a motor 42 driving acam 16a and a rocking lever 1Gb. The cross-slide is carried on a saddle17 which is continuously traversed along the workpiece (by means notshown) along a slideway 20.

A pneumatic measuring head 18 is mounted at the top of a rigid frame 19rigidly connected to the saddle 17. From the bottom end of this frameprojects an anvil 21 which bears against one end of a diameter of therotating workpiece in the plane of that particular circumference onwhich the grinding wheel 13 acts, whilst the feeler 22 of the measuringhead 18 bears against the opposite end of the same diameter. Air issupplied at a standard pressure of 3% pounds per square inch by airsupply unit 23 through air lines 24, 25 and 26. Air line 24 feeds air tothe measuring head 18, and changes of diameter of the workpiece move thefeeler 22 axially, which alters the drop in pressure across an orificein the head 18. The resultant modified air pressure is a measure of thediameter of the workpiece with respect to the datum diametercorresponding to the position of the orifice, and this pressure istransmitted through an air line 27 to pressure comparison apparatus 28.This apparatus compares the modified pressure in the air line 27 (givinga measure of the workpiece diameter deviation) with the standardpressure in air line 25 by means of a pair of differential bellows 29,31 to which air at standard pressure and modified pressure is supplied,respectively. The resultant mechanical movement of the bellows as themodified air pressure changes is converted (by means 32 including adifferential transformer 36-see FIG. 9) into a varying electrical signalwhich is fed into the grinding machine control amplifier 33. A similarpair of differential bellows 29a, 31a operate a pressure gauge 34 whichindicates on its dial the deviation in the workpiece diameter i.e. thedifference between its actual diameter and the predetermined datumdiameter.

The rate of grinding of the workpiece 12 by the grinding wheel 13 ismeasured by measuring the load on the wheel motor 14, which in this caseis an alternating current motor. The current taken by the motor 14 isarranged to pass through the primary winding 35d of a transformer 35,the secondary winding 3517 of which provides an alternating voltagesignal at mains frequency proportional to the wheel motor current,

The various signals are fed into an input network, the circuit diagramof which is shown in FIG. 9. This input network is incorporated with anamplifier, the circuit diagram of which is shown in FIG. 8, to form thegrinding machine control amplifier 33.

The input network shown in FIG. 9 includes resistors R1-R7, variablepotentiometers 38, 41, 43 and 45, capacitors C1-C4, transformers 36 andT1, and a self-latching relay 46 with operating buttons 47 and 48 andcoil L1.

The remainder of the circuit of the amplifier 33 is shown in FIG. 8 andincludes thermionic valves VlA, V1B and V2 of type ECC81 and V3 and V4of type EL90, resistors R8-R21, variable potentiometer 44, capacitorsCS-Clfl, transformer T2, and inductance L2.

Referring now to FIG. 9, an A.C. signal of 6 volts at mains frequency isfed in at the terminals A-A, and through a resistance network 37including a potentiometer 38. A voltage tapped off across thepotentiometer 38 is applied to the primary winding 39 of differentialtransformer 36 similar to transformer 308 previously described, of theconverting means 32. The armature of transformer 36 is coupled to thebellows 29, 31 so that as the latter move, an output signal representingthe diameter deviation is obtained.

The alternating voltage from the transformer 35 representing thegrinding motor load is injected into the input network at terminals B-Band through transformer T1. A further signal at mains frequency isapplied to the terminals C-C in order to cancel out that part of themotor load signal which represents the no-load condition of the grindingwheel, so that the resultant signal represents the mechanical load onthe grinding wheel 13. By altering the potentiometer 41, the no-loadcancelling signal may be adjusted to an experimentally determinedcorrect value.

A further signal is applied, in opposition to the load signal, atterminals D-D of the input network which are connected to the terminalsDD-DD at the output end of the grinding machine control amplifier (seeFIG. 8). This signal represents the velocity with which the grindingwheel 13 is fed into or backed off from the workpiece by the motor 42 ofthe feed mechanism 16. The negative feed back thus provided overcomesinertia effects in the system and checks any tendency to hunt about theno signal, position. The signals derived from inputs at terminals C-Cand D-D may both be adjusted by means of potentiometer 43 in the inputnetwork, whilst the feed back to input at D-D may also be adjusted bypotentiometer 44 (see FIG. 8). The potentiometers 38 and 41 controlrespectively the maximum and minimum grinding wheel loads which arepermitted by the control system, and are provided with calibratedcontrol knobs 109 and 1.11 respectively (FIG. 7).

An over-riding manual control for controlling motor 42 to back-off (i.e.withdraw) the grinding wheel from the workpiece is provided in the inputnetwork. For this purpose a mains frequency voltage of 6.3 volts isapplied to terminals H--H and through an adjustable potentiometer 45 insuch a way that, when the resultant voltage appearing at the terminal Fis applied to the grid of the second stage of the amplifier 33, theamplifier controls the motor 42 to back-off the grinding wheel. Aconventional self-latching relay 46 is employed, powered by 300 voltsD.C. When the button is pressed, contacts 49 are held closed, connectingthe point F to the point G on the amplier 33 (see FIG. 8), until thebutton 48 is pushed. The output of the input network at terminal JJ isfed into the main amplifier at terminal J.

Referring again to FIG. 6, the output of the grinding machine controlamplifier 33 drives a motor 51, which is mechanically coupled to asynchro transmitter 52. This transmitter drives the motor 42 which feedsand backs off the grinding wheel 13 to or from the workpiece. Thecontrols of the input network and the main grinding machine controlamplifier are set so that, when button 48 has been pressed the amplifiercontrols the motor 42 so that it feeds or backs-off the grinder wheel sothat the rate of grinding varies with the deviation of the workpiecediameter from the predetermined datum diameter. When the button 47 isdepressed, the relay coil L1 is energised The desired datum diameter forthe workpiece is altered Y by adjusting the pneumatic workpiecemeasuring head 18. As the position of the aforesaid orifice within thehead is altered along the direction of movement of the plug connected tothe feeler 22, so the zero or datum position, with respect to which thehead measures the diameter deviation of the workpiece moves. The orificeof the head 18 is moved by a zero-set synchro receiver motor 61 drivenby a transmitter 62. Connected in parallel with the motor 61 is asimilar zero-set motor ,63 so that the latter adjusts the zero-positionof pneumatic reference head `64 identically and simultaneously with thezero-position of the measuring head 18 adjusted by the motor 61. Thusthe zero-positions of the measuring head 18 and the reference head 64are always the same. The zero-positions of the heads are set to therequired positions by setting mechanically the position of the feeler 65of the reference head 64 to correspond to the -desired datum diameter ofthe workpiece, and arranging that the air-pressure output signal fromthe reference head controls the zero-set transmitter 62 to set thezero-positions of both heads so that the reference head shows nodifference between its zero position and the measured position of itsfeeler 65. Thus the zero-position of the measuring head 18 iscontinually adjusted to correspond to the desired datum diameter set bythe position of feeler 65 of reference head 64.

The means for enabling the output signal from the reference head tocontrol the transmitter 62 are generally similar to those describedabove which enable the signal from measuring head 18 to controltransmitter 52. The air pressure signal from the reference head 64 isfed into a pressure comparison apparatus 66 similar to the apparatus 28,and including differential bellows 67, 68 into which the standardpressure from air-line 25, and the modified pressure from air-line 26(i.e. the air pressure signal from head 464), are introducedrespectively. The resultant mechanical movement of the bellows as themodified air pressure changes is converted into a varying electricalsignal by means y69 (similar to means 32) which includes a differentialtransformer 71.

This varying electrical signal is fed into a zero-set control amplifier72 which incorporates an input network circuit diagram which is shown inFIG. This input network includes the differential transformer 71, avariable potentiometer 75, and a capacitor C11. The circuit diagram ofthe remainder of the amplifier 72 is shown in FIG. 3, the amplifiers 33and 72 differing only in their input networks. The terminal JJ] of thisinput network is connected to the terminal I 0f the main amplifier 72.The armature of the differential transformer 71 is moved by bellows 67and 68 with respect to its primary and secondary windings, thus alteringthe voltage induced in the secondary windings due to an alternatingvoltage of 6 volts applied to the primary winding 73 at terminals AA-AA.A further signal is applied at the terminals DDD-DDD of the inputnetwork, which are connected to the terminals D-D at the output end ofthe zerset amplifier 72. This signal represents the rate of rotation ofthe motor 74 which the amplifier controls. The negative feed-back thusapplied to the amplifier 72 ensures stability of the system. The amountof feed-back may be adjusted by means o-f the potentiometer 44 in theoutput end of the amplifier 72, and by means of the potentiometer 75 inits input network. The output of the zero-set amplifier 72 drives amotor 74 which is mechanically coupled to the synchro transmitter 62.The transmitter 62 drives the zero-set motors 61 and 63 as aforesaid.

In order to grind workpieces with tapered or cambered profiles, meansare provided for varying the desired datum diameter of the workpiece asthe grinding wheel traverses the workpiece, by varying the position ofthe feeler 65 of the reference head 64 in a predetermined manner as thegrinding wheel moves along the slideway This apparatus is representedconventionally at 76 in FIG. 6 and is shown diagrammatically in greaterdetail in FIG. 7. This apparatus is exactly the same as that indicatedat 276 in FIG. 1, where feeler 261 of the reference head 264 correspondsto feeler of reference head 64. The description of the apparatus at 76applies equally to both embodiments.

The end of the reference head feeler l65 rests on a cross arm 7-6, nearone of its ends 77 at which it is slung resiliently on a spring strip`83. At its other end 78 the arm is urged downwardly by a spring 79 andis adjustably supported by a fiexible steel tape 81 wound around andattached to a datum set spindle 82. Resiliently attached to the end 77of the cross arm by a spring strip 86 is the lower end of a pick offar-m I84, which is supported by a spring 85, providing support for theweight of arms 84 and 76, together with the reaction of the feeler 65.The arm 84 is provided at `itsirpper end with a roller 87 and can pivotabout its lower end on the spring strip 86, the roller 87 moving alongthe underside of a cam follower arm 88 which is pivoted at one end 91.Near its uper end the arm V84 is attached to one end of a spring 89which tends to move its upper end away from the pivot 91, and isadjustably retained in a substantially upright position by a flexiblesteel tape 92 which is wound around and attached to set percentagecamber spindle 93. The end of the cam follower arm 88 remote from itspivot 91 is provided with a roller 94 which bears on the periphery of acam 95. The roller is urged into contact with the cam by a. spring 96attached to the shaft near the roller.

It will be apparent that as the cam rotates, the cam follower arm 88will rotate to a certain extent about its fixed pivot 91. The roller 87is in contact with the arm 88 at some point near its pivot 91, so thatthe arm 84 is moved in a direction more or less along its own length, byor against the urging of its supporting spring 85. The proportion of themotion of the cam follower roller 94 transverse to its arm 88 which isimparted to the arm 84 as longitudinal motion depends upon the relativedistance of the rollers 94 and 87 from the pivot 91 i.e. upon theposition of the roller 87 along the cam follower arm 88. This variableposition is set by rotating the set percentage camber spindle 93 so thatthe flexible tape 92 restrains the arm 84 in the desired transverseposition against the urging of the spring 89. The longitudinal positionof the arm 84 is transmitted to the end 77 of the cross arm 76 as motionof that end transverse to the arm 76, the spring strip 83 allowing suchmotion The transverse position of the other end 78 of the cross arm isdetermined by the angular position of the datum set spindle 82, whichcontrols the length of the tape 81 which extends from the spindletransversely of the arm 84 to support the end 78 against the urging ofspring 79.

Thus the longitudinal position of the feeler 65 of the reference head 64depends upon (a) the angular position of the datum set spindle 82 and(b) the longitudinal position of the pick off arm 84. The last-mentionedposition further depends upon (c) the angular position of the setpercentage camber spindle 93 and (d) the angular position of the cam 95.

The cam 95 is rotated through gearing 102 by a synchro receiver motor97, which is driven by signals from a punched tape digital controlapparatus, indicated diagrammatically at 390, the operation of whichwill be described in detail below. The control apparatus is driven bysignals from a synchro transmitter 98 mounted on the grinding machinesaddle 17. A pinion wheel 99 is mounted on the shaft of the transmitter98 and engages with a rack 101 fixed relative to the slideway 20. As thesaddle is traversed along the slideway 20, the shaft of the transmitter98 is rotated by an angular amount proportional to the saddle travel.Thus the cam 95 is rotated automatically, as the grinder wheel 13traverses the workpiece, in a manner depending on programme employed onthe punched tape used in the control apparatus 390. The shape of the cam95 is such that the changes of position of the feeler 65 of thereference head, as the cam 95 rotates, produces the desired change ofdesired datum diameter, and thus causes the grinder to grind theworkpiece 12 to the desired cambered profile. The camber produced isdetermined by the control apparatus, as will be described below, but maybe reduced proportionately by setting the angular position of the setpercentage camber spindle 93 so that the roller 87 is nearer to thepivot 91, a calibrated scale being provided for that purpose. Inparticular, when the roller 87 is opposite the pivot 91, the arm 84 willremain stationary as the cam revolves, and no camber will be produced onthe workpiece 12. The initial datum diameter for the workpiece is set byadjusting the angular position of the datum set spindle 82. Further areversing switch 103 is provided to reverse the sense of rotation of themotor 97 with respect to that of the transmitter 98, so that increasingand decreasing cambers may be ground along the length of the sameworkpiece 12 with the same cam 95 whilst the saddle 17 is traversing inthe same direction. Reference to FIG. 1 shows a corresponding switch220', mounted on the saddle 216, which may be operated by contact with astriker 220a when the saddle is in an appropriate traverse position withrespect to the workpiece. If a symmetrically cambered roll is required,e.g. one which tapers at its ends, the switch 220 is arranged to beoperated when the grinding wheel is at the centre of the workpiece. Cam95 is arranged to rotate to its full extent for half the traverselength. At the half-way point, switch 220 changes the relative sense ofrotation of the cam 95 with direction of movement of the saddle. Thecam, having rotated to its full extent then reverses in direction ofrotation and ensures a symmetrically ground workpiece, the same camhaving been used for both halves of the workpiece.

In order to provide a permanent record of the variation of the diameterof the workpiece along its length, there is provided a conventionalchart recorder 104 (conveniently mounted on the cabinet of the airsupply unit 23). The recording pen 105 of the recorder moves under thecontrol of a diameter deviation indicator (not shown) similar to the one34 already described, and the rotation of the chart is produced by amotor (not shown) driven by the synchro transmitter 98, so that angularrotation of the chart corresponds to traversing of the measuring head 18along the workpiece.

There is also provided an indicator 106 driven by a receiver motor 107which is electrically coupled to the transmitter 52 to indicatecontinuously how far the grinding wheel is fed towards the workpiece. Anammeter 108 is provided, to indicate the current passing through thegrinding wheel motor 14. An indicator 112, driven by the zero-set motor63 of the reference head 64, gives a continuous indication of theinstantaneous value of the predetermined datum diameter.

The method of operating the machine is as follows. A blank oversizedworkpiece is mounted in the grinding machine. The datum set spindle `82is set to obtain an indication of zero diameter deviation at the desireddiameter of the finished workpiece. If a plain i.e. uncambered roll isrequired, the set percentage camber spindle 93 is set to indicate zeropercent, i.e. the roller 89 is at the pivot point 91. If a cambered rollis required, a cam 95 having a suitable profile is selected, and the setpercentage camber spindle 93 is set to indicate the desired percentage(calculated from the total camber produced when 100% camber is set).'Ihe switch 103 is used for synchronising the cam zero with theappropriate traverse position.

The various pre-set controls in the ampliers 33 and 72 or 236 and 242are set to give the control system the required characteristics.

The maximum and minimum wheel load potentiometers 38 and 41 are set tothe required values. For example, the maximum wheel load potentiometer38 may be set so that the ampliiier allows the full load on the grindingwheel to be applied for a deviation in the diameter of the workpiece of.001 inch or more. The minimum wheel load potentiometer 41 may be set sothat the ampliiier allows 5% of the full load to be applied for zerodeviation.

The workpiece 12 is set in rotation and the automatic control systemswitched in to ensure, in the manner described, that the rate ofgrinding decreases as the workpiece 12 diameter approaches the desireddimension. The grinding wheel 13 is traversed along the workpiece 12 ata rate which is slow enough for the above-mentioned relationship to bemaintained by the control system, whether the desired datum diameter isconstant (for a plain roll) or varies (for a cambered roll). In thelatter case, the datum diameter is automatically varied by the cam andits associated mechanism, as previously described. In order that a rollmay be produced having a double camber, i.e. a roll which is thicker atits centre and decreases in diameter towards its ends, the camber motorreversing switch 103 or 220 enables the same cam 95 to generate the twocambers in different directions, the saddle 17 moving in the samedirection, and the transmitter 98 rotating in the same direction, duringthe cutting of Iboth cambers. The switch 103 or 220 is positioned on thegrinding machine so that it is automatically operated at the correctpoint in the traverse as the saddle 17 passes it.

The general construction and operation of the machine now having beendescribed there will now be described the manner of operation of thepunched tape digital control `apparatus indicated at 389 in FIGS. l to 5and 390 in FIGS. 6 to 10. Reference will be made only to the embodimentof FIGS. 6 to 10 and it will be understood that the control apparatus389 in the embodiment of FIGS. 1 to 5 operates in a similar manner tothe control apparatus 390.

The control apparatus 390 is digital in character, the digits concernedbeing the steps in a step-by-step programme recorded on punched papertape, so that any programme is indefinitely repeatable within the limitsof accuracy set by a single digit. Such limit can readily be madenegligible. The control apparatus satisfies two main requirements.Firstly, by employing a suitable punched tape the time taken for the cam95 to perform one revolution may be matched to the time taken for thegrinding wheel 13 to be traversed the -full length of the workpiece,since this latter time will, of course, vary according to the length ofthe workpiece. Secondly there is a requirement to produce at 'willcamber forms (eg. para'bola, ellipse etc.) according to laws other thanthat to which the cam 95 has been cut. This can be achieved by employinga suitable programme on the punched tape to vary the cam profile byvarying the rate of rotation of the cam 95 as it rotates.

In the control apparatus 390 the punched paper tape is fed forward andbackward through a reading machine, in step with the traversing head ofthe grinding machine. A separate tape is required for every roll lengthfor which a complete rotation of the cam 95 is desired, and the lengthof any tape will ybe proportional to the length of its correspondingroll. The tape will carry a pattern of punched holes, Iwhich as theypass through the reading machine will generate the standard successionof step by step signals for driving motor 97 of the camber cam 95. Byrst generating more signals than are required for complete rotation ofthe cam 95, onward stepping sign-als may be interspersed with standstillsignals to produce a cam movement that bears any required relation tothe traverse movement of the grinder Wheel 13.

As mentioned abo-ve the traverse position step by step transmitter 98drives the paper tape through a reading head 'by a sprocket such thatthe tape is positively driven, and will be moved back and forth, onestep at a time, by the traverse transmitter signals. The step movementof the tape is such as to laccommodate a row of six punched holes acrossits width, and typical arrangements are shown in FIGS. 11 and 12. Of thesix positions, either two or three are punched at any station, andtwelve of the possible arrangements of such holes in the six availablepositions can be used to generate the twelve characteristic andsuccessive step lby step switching patterns. While the following moredetailed description gives in the simplest terms an elementary workingsystem, any of the commonly available paper tape systems of a moresophisticated character, and better suited to computer punching, may beemployed.

lLet the maximum roll half length be R", and the minimum half lengthrequirement be r. Let the total number of step by step signals now.generated by the traverse in traversing a distance R be N. Then thenumber of step by step signals to give full rotation of the camber camwill also be N.

The traverse transmitter is geared to deliver R/rXN step -by stepsignals in the course of a traverse of R", and these signals are used tostep forward the paper tape. In the course of NR/ r steps of the tape,the cam 95 receives N steps only, equally spaced, or with anirregularity not exceeding one step about the mean. NR/ r-N steps of thetape must produce no steps of the cam. Following any step by step signalpunched in the tape, in the sequence 1-12 shown in FIG. l1, there mustbe R/ r-l repetitions of the same signal before a change is made to thenext signal pattern of the sequence, which is again to be followed bythe same number of repetitions before the next change. This instructionholds for any value of r, say r', between r and R. It is clear that thevalue of R/ r--1 is unlikely to be a whole number, and if it is not,then the whole number above or lbelow the nearest whole number must bealternated with it in a calculated pattern so that over a completetraverse the difference between the number of required and actu-al camstep signals does not exceed one at any time. Such a programme willallow a half traverse of r, yielding NRr/ r steps to deliver N steps tothe cam and thus produce a complete rotation at la rate very closelytied to the traverse rate.

To meet the requirement of providing for different camber laws whileusing the same cam, it is necessary to note the cambers yielded by thecam at points along the traverse. It is then necessary to calculate thedifferent points along the traverse at which these cambers are requiredunder the new law. This creates a demand for a particular camber to bereached earlier at one point and later at another than would be reachedby uniform rotation of the cam 95. With a programme tape runningsynchronously with the traverse, |with a greater rate of stepping thanis needed to complete the cam rotation, it merely ybecomes a matter ofomitting occasional scheduled repeat punchings to bring the cam forwardmore quickly,

or to introduce additional intermittent duplications of punch pattern,so that the cam rotation is held back, thus decreasing the rate ofcamber. If such a modied camber track is to be laid out, as it clearlycan be, within an error limit of a single step, a computer is anecessity for its preparation.

A suitable form of tape reader is shown in FIGS. 13, 14 and 15. The tapereader comprises a step by step motor 391 mounted on a support 392. Themotor 391 drives a gear wheel 393 which in turn drives an idler wheel394. The idler wheel 394 drives directly gear wheels 395 which rotatetape driving sprocket wheels 396 mounted on the .opposite side of thesupport.

Co-axial with the idler wheel 394 are co-axial sprocket wheels 397 whichdrive further sprockets 398 through endless chains 399. Co-axial withthe sprockets 398 and connected to them through free wheel and slippingclutch assemblies are tape spools 400.

Punched paper tape extends from one spool 400 to the other across thesprocket wheels 396 and, as best lseen in FIG. 13, between the sprocketwheels 396 the punched tape passes over a fixed support 401. A cavity402 vis formed in this support 401 and extends4 across the full width ofthe paper tape. The cavity is covered by a window 403 and disposedwithin the cavity, yspacedy across the width of thepaper tape, are sevenphoto diodes, photo transistors, generating cells or similar lightsensitive devices. The devices are so disposed that each underlies onerow of punched holes in the paper tape.

A lamp 404 is mounted on the support 392 and light from the lamp isreflected downwardly on to the light sensitive devices by means of aprism 405. A window 406 is provided in the support 392 between the lamp404 and the prism 405.

There are twenty four tape engaging tags on each sprocket wheel 396 andthese engage a continuous line o f perforations 407 (see FIGS. 11 and12) whichextend along a part of the tape not used for signalperforations.

The step by step motor 391 rotates at twenty four steps per revolutionand each step of the motor will carry the tape forward (or backward)according to the succession of step by step signals received by it fromthe transmitter 98. The distance moved by the tape at each step will beslightly more than is needed for a transverse row of holes that arepunched in the tape to generate coded signals. Any holes punched inthetape must always lie above one or more of the light sensitive devices inthe cavity 402. Light is able to reach a light sensitive device freelyonly when a punched hole lies over the device. Each light sensitivedevice is arranged in known manner, with or Without an associatedamplifier, to energise a relay to close a pair of contacts. The sevenlight sensitive devices and their associated seven relay contacts form acomplete step by step transmission system, and the system will providethe three field terminals of the step by step receiving motor 97 withenergisation for step by step rotation in a manner determined by theprogramme punched on the tape.

The tape punch pattern at each step is always one of the arrangementsnumbered 1-12 in FIG. 11 and if any pattern repeats itself in successivesteps, the receiving motor 97 will remain stationary. If the patternchanges, it must change only to the next higher or lower numberedpattern in the 1-12 sequence according as the desired motor rotation isin one direction or the other. The next step beneath 1 is of course 12,and the next step above -12`is -1.

A separate tape is run off by computer for cambered Workpieces ofdifferent length, and/or, for each"differ ent camber law. It might Wellbe considered that a particular tape belonging to a roll of certainlength would be perfectly suitable for use on another roll only slightlyshorter. In practice there is a distortion of the camber law throughfailure to complete the rotation of the cam.

Many commercial computers are equipped with a device for punching papertape as a means of temporarily or permanently recording particularcomputations. `It is envisaged that such a computer could, be ,employedto prepare paper tapes for control of the grinding machine.

A tape required to :grind a workpiece of half length r, where thegrinder traverse transmitter generates-step by step signals at a rate ofS steps per inch of traverse, must have a total of Sr punch positions,and this determines the length of tape. If the cam requires N steps torotate through its full working profile, then Sr punch positions in thetape must yield N step transmissions to the camber cam drive. To producesuch a tape, the computer isV programmed to punch out the pattern 1-12of FIG. 1-1 repetitively N/ l2 times, spread as uniformly as possibleover Sr punch positions, the gaps being lled in by repetition of theimmediately preceding signal pattern.

T o produce a tape which will cause the grinder control to generate acamber law other than that generated by rotating the cam in synchronismWith the grinding traverse, it is necessary to set up in the computermemory a mathematical formula from which the computer can derive thedesired camber coordinate for each of the Sr steps along the tape. Intoanother memory of the computer is placed the formula for the cam used inthe grinder control. The computer is then programmed to punch out a tapecontaining Sr punch positions, again giving N/l2 repetitive sequences ofthe pattern 1-12 of FIG. 11.

At each step of the tape, the computer compares the desired camber withthe camber produced by the cam. If the camber produced by the cam isequal to or greater than the desired camber, any existing step by steptransmission is maintained by repetition of the punch pattern. When thecamber produced by the cam is found to be less than the desired camber,then the punch pattern changes at the rst opportunity. Thus the desiredcamber is matched by the advanced or delayed positioning of the cam,within a limit of a single step.

The tapes may be stored and operated in cassettes of the kind commonlyused for amateur cine film. These would be placed in the tape readingmachine so that an exposed and marked part of the tape provides areference point, which is linked to the centre or end of the workpiecewhere a tape reversal will normally take place. The tape drive sprocketsystem engages with the tape at this point and remains engaged until thecassette is nally removed at the completion of the grind. This removalis done once more at the centre or end of the workpiece, so that themarked point of engagement is visible.

As the tape is driven forward by the sprocket drive, the tape that haspassed through the reading head is coiled up in the reel-up sprocket ofthe cassette, by a lightly engaged friction drive. The unread tape isdrawn from the un-reel pocket on the opposite side, and the reelingmechanism is allowed to free-wheel. When the sprocket drive is reversedas the grinding machine traverse is reversed or as the centre line ofthe roll is crossed, so the tape direction is reversed, and the drivingarrangements to the reel-off and reel-up cassette pockets are reversed.

I claim:

1. A grinding machine comprising:

(a) a grinding wheel for grinding a circumferential surface of aworkpiece of circular cross-section;

(b) traversing means adapted to effect relative longitudinal traversingmovement, in the direction of the axis of the workpiece, between thegrinding wheel and the workpiece;

(c) rotary means for rotating the workpiece while it is being ground;

(d) gauging means for determining, while the grinding wheel is grindingthe workpiece, any difference between a datum value and the diameter ofthe particular circumference of the workpiece on which the grindingwheel is acting;

(e) means, controlled by the gauging means, for adjusting the positionof the grinding wheel in a sense to bring said difference to apredetermined value;

(f) a movable datum member providing said datum value;

(g) a cam rotation of which is adapted to effect ad justment of theposition of said datum member, thereby adjusting the datum value;

(h) control means, actuated by the traversing means, and controlling thecam-driving means in a manner to relate the rotational position of thecam to the position of the traversing means;

(i) the control means being adjustable in a manner to vary the relationbetween the rotational position of the cam and the position of thetraversing means.

2. A grinding machine according to claim 1 wherein the control meanscomprise:

(j) an information carrier;

(k) reading means past which the information carrier is moved;

(1) drive means for moving the information carrier past the readingmeans;

(In) the drive means/ being controlled lby said `traversing means so asto move in synchronism therewith;

(n) the reading means controlling the cam-driving means in accordancewith a predetermined programme carried by the information carrier.

3. A grinding machine according to claim 2 wherein the drive means forthe information carrier comprises a synchro receiver motor driven by asynchro transmitter which is driven in turn by the traversing means.

4. A grinding machine according to claim 3 wherein the traversing means,synchro transmitter, synchro receiver motor, and information carrier areall driven 'with a step-by-step motion.

5. A grinding machine according to claim 4 wherein the cam-driving meanscomprise an electric motor driven with a step-by-step motion by signalsimparted to the reading means by the information carrier.

6. A grinding machine according `to claim S wherein the informationcarrier comprises punched tape.

References Cited UNITED STATES PATENTS 3,088,250 5/1963 Hold et al.51-165 3,321,869 5/1967 Parrella et al 51-49X 3,391,497 7/1968 Parrellaet al. 51-165 LESTER M. SWINGLE, Primary Examiner U.S. Cl. X.R. 51-165 i

